Device for grinding the slideways of machine tools



Nov. 12, 1957 o. BRETscHER DEVICE FOR GRINDING THE SLIDEWAYS OF MACHINETOOLS Filed Sept. 8, 1955 INVENTOA" 1 0770 @BETH/ffl? United StatesPatent ce 2,812,620 `Patented Nov.` 12, 1957 DEVICE FOR GRINDING THESLIDEWAYS F MACHINE TOOLS t Application September 8, 1955, Serial No.533,186

Claims priority, application Switzerland September 11, 1954 6 Claims.(Cl. 51-45) The present invention relates to a device for grinding theslideways of machine tools, particularly lathe beds, as well as thetable beds of grinding, milling and planing machines. These beds do notas a rule bear on the foundation along their entire length with theresult that between the surfaces bearing on the foundation bridges areformed which may sag under the operating load. Even if this sag isrelatively small, there is still the possibility that the workpiecehandled on the machine is not sufficiently accurate.

To eliminate this drawback, the suggestion has been made to machine theslideways under an initial bending stress in such a way that theslideways are curved in their longitudinal direction when unloaded andlinear when loaded, i. e. in the operating condition. It is, however,difficult to achieve by means of this curved tensioning of the slidewayan arch which will be flattened out at a certain load.

. The presentv invention aims at providing a device by means of which anarch of the slideways, which is accurately determinable in advance, canbe ground in their longitudinal direction. The invention consists in thefact that means are provided to raise and lower the grinding wheelduring its travel across the slideway in such a way that the said wheeldescribes an arc, the chord length of which corresponds to the length ofthe -slideway to be ground and the rise of which corresponds to the sagrequired.

Two embodiments of a device according to the invention are illustrated,by way of example, in the attached drawing, in which:

Fig. l is a lateral partly sectional View of a device for grindingslideways, wherein a grinding wheel support is arranged to oscillate oneccentric journals of a rotatable shaft which is turned by a motor inorder to move the grinding wheel up and down;

Fig. 2 is a partly sectional view of the same device in which the upwardand downward motion of the grinding wheel is produced by the lattersinfeed motor; and

Fig. 3 is a circuit diagram for the control of the motor which causesthe upward and downward motion of the grinding wheel.

Referring now more particularly to Fig. 1 of the attached drawing, agrinding attachment is shown in which the support 1 of the grindingwheel spindle 2 is suspended on eccentric journals 3a of a rotatableshaft 3. Secured to the shaft 3 is the lever 4 which, by means of themotor 7 acting via a threaded spindle 5 and the worm gearing 6, turnsthe shaft 3 a few degrees to either side out of its central position, inwhich the axis of the eccentric journal 3a is vertically beneath theaxis of the shaft 3, so that the grinding wheel 8 is moved a littletowards or away from the workpiece 13 according to the position of thelever 4. The speed of the table driving motor 11 (Fig. 3), serving toprovide the longitudinal motion of the table 12, on which the workpiece13 rests, and the speed of the motor 7 bear a certain relationship toeach other which can be electrically or mechanically adjusted. Thisratio determines the rise of the slideway arch on the workpiece 13.Reversing the direction oftable 12, also changes the direction ofrotation of the :motor 7 and thu-s of the lever 4, as described inconjunction with Fig. 3. The selective transmission ratio between thetable driving motor 11 and the motor 7 can also be replaced by a txedratio. In this case the length of the elfective arm of the lever 4 canbe altered by sliding the driving unit 5 to 7 upV or down, thus alsomaking it possible to'adjust the rise of the workpieces slideway arch.

The spindle 8a, the gearing 9 and the infeed motor 10 serve merely toswing the support 1 in and out in order to feed in the grinding wheel 8in accordance with the amount of stock to be removed.

A second embodiment of the device for obtaining a longitudinally archedslideway is illustrated in Fig. 2. In this embodiment the swivelling ofthe support 1, which is used to feed in the grinding wheel automaticallyfor `the purpose of removing stock, also serves to raise and lower thegrinding wheel for the purpose of producing the arc. As in Fig. 1, thesupport 1 is arranged to rotate about the shaft 3b, the journals 3c ofwhich are not disposed eccentrically. In the device shown in Fig. 2 thespindle 8a, the gearing 9 and the infeed motor 10 serve not only to feedin the grinding wheel in accordance with the amount of stock to beremoved, but at the same time to raise and lower the wheel 8 duringgrinding and to produce an arched way.

To produce an arched slideway, the infeed motor 10 is so controlled inthe case of this device that the support 1 is swung out about the shaft3b via the gearing 9, whereby the grinding wheel 8 is raised, thusproducing the difference in the rise of the arch of the surface to beground.

While the workpiece 13 is displaced beneath the grinding wheel 8, whichis driven by the motor 11, until the workpiece centre M is verticallybelow the grinding wheel axis, the grinding wheel 8 is raised andlowered by swivelling as the table is moved to its terminal position atthe initial height. During the reciprocal motion the infeed motor issimultaneously lowered to the zero position, at which the theoreticalsize is attained.

The wiring diagram (Fig. 3) shows the control of the table driving motor11 and of the infeed motor 10 or 7. A direct-current generator 15 withtwo exciting windings 16 and 17 is coupled to the table driving motor11. The excitation of the infeed motor 10 or of the motor 7 is set at anadjustable direct-current voltage applied to winding 18. Thetransmission ratio between the table motor 11 and the motor 7 cr 10 canbe adjusted with the aid of the regulating transformer 19 by alteringthe generator exciting voltage. If the regulating transformer is stillfurther adjusted via a cam disk, independently of the table motion, bymeans of the same device as the regulating transformers 20a and 21a, theshape of the grinding curve can be influenced by the shape of the camdisk. This could also be effected by a mechanical or iniinitely variablegear. The current collectors 20 and 21 of the regulating transformers20a and 21a are adjusted together from Zero to maximum or from maximumto zero for the grinding length by the table motor 11 or, mechanically,by the motion of the work-table 12. By means of an adjustable couplingthe central position of the two current collectors cani be brought intoregister with the centre of the grinding length. At the start of thetraverse of the work-table 12 the current in the exciting winding 16 isat its maximum and in the other winding 17 at zero. The generatorvoltage is thus at its maximum and therefore the speed of the motor 7 or10 as well.. In the middle of the traverse the exciting current in bothcoils is equal. As, however, the current ows through these coils inopposite directions, the generator excitation is zero and thus thegenerator voltage and the speed of the motor 7 or 10 are also zero. Whenthe work-table continues its travel, the current in the exciting winding17 is preponderant. Thus the direction of the rotor current' in thegenerator and motor 7 or 10l1as been reversed and the motor 7 or 10 runsin the opposite direction and; again attains its maximum speed in theterminal position of the Worktable. Now, as the direction of the tablemotion changes, the direction of rotation of the generator is alsoreversed and thus they motor '7- or 1G also runs at maximum speed in theopposite direction and the cycle begins again in this direction.

The device described can be employed wherever a motor is used forfeeding in the grinding wheel.

Various changes and modication-s may be made without departing from thespiritl and scope of the present invention and it is intended that suchobvious changes and modifications be embraced bythe annexed claims.

Having t-hus described the invention, what is claimed as new and desiredto be secured by Letters Patent, is:

1f. A device for grinding substantially flat workpieces sol as to archsaid workpiecs in at least one direction, comprising a rectilinearlyreciprocal work table for supporting a workpiece, a grinding wheel, asupport located above saidy table and rotatably carrying said grindingwheel, means mounting said support fork angular reciprocal movementabout an axis for adjustment of the elevation of said grinding wheelabove said work table, reversible -electric motor means operativelyconnected to said support for angularly moving the sameto effect saidadjustment of elevation of said grinding wheel, and an electricalcontrol system responsive to displacement of said work table andconnected tosaid electric motor means for regulating theelevation-adjusting operation of the latter in dependence on the motionof said work table, whereby each workpiece may be ground with a highdegree of precision,

2. A device according to claim 1, the perpendicular distance betweensaid axis and the workpiece-supporting surface of said table beinglinvariable.

3. A device according to claim 1, said control system including meansfor chan-ging the speed of rotation and the direction of rotation ofsaid `electric motor means in accordance with said motion of said worktable.

4. A device according to claim 1, further comprising additionalreversible IelectricV motor means operatively connected to said worktable for: reciprocally displacing the same, and a D. C; generatorcoupled to said additional electric motor means and connected in circuitwith said first-named electric motor mea-ns for energizing the latter inaccordance with theA operation;` of said additional electric motormeans.

5. A device .accordingr tor c1'a-im.4 said control system including anenergization circuit for said generator, and means operated by saidtable during displacement thereof for controlling the electric currentflow in said energiza.- tion circuit.

6. A device according to claim 1, further comprising a. rotatable shaftprovided' witlrat least one eccentric` bearing portion, `said grindingwheel support being; pivotally` carried by said` eccentric bearingportion, a lever fixed to and extending at an angle from said shaft,`and. transmission means interconnecting said electric motor means with apart of said lever spaced from the junction of the latter with saidshaft, whereby upon angular displacement of said lever and consequentrotation of :said shaft the elevation of said support together with saidgrinding Wheel relative to said work table is adjusted due to movementof said eccentric bearing portion about the axisv of said shaft.

References Cited: in the tile of this patent UNITEDI STATES PATENTS

